When delivering pacing stimulation to the left ventricle of the patient's heart, it is beneficial to provide the pacing in the endocardium so as to achieve synchronized heart beats as the activation time of the left ventricle is reduced compared to epicardial pacing. In both cases, it is the myocardial cells adjacent to the endo- and epicardium, respectively, which are stimulated, not the endocardium or epicardium.
The subendocardial muscle is a thin layer, about half a millimeter thick. A stimulation electrode should be placed close to this layer in order to take advantage of the positive effects of pacing the myocardial cells close to the endocardium. Placement of an endocardial lead via the left ventricle is characterized by an increased risk of thromboembolic events. Endocardial pacing of the left ventricle can be achieved by a transseptal pacing lead via intraventricular septum, eliminating the risk for thromboembolic events by lead exposure in the blood flow of the left ventricle.
However, placement of an intramural pacing electrode via septum for the purpose of endocardial stimulation should therefore be close to the endocardium to ensure similar performance to an activation fixation lead implanted from the endocardial side. When placing the pacing electrode via septum, it is thus very important that the position of the electrode relative to the septum can be determined with a high degree of accuracy.